Method of extruding fused thermoplastic compositions



H. DREYFUS 2,370,721

METHOD OF EXTRUDING FUSED THERMOPLASTIC COMPOSITIONS March 6, 1945.

-F'iled Jan. 24, 1941 Patented Mar. 6, 1945 METHOD OF EXTRUDING FUSEDTHERMO- PLASTIC COMPOSITIONS Henry Dreyfus, London, England, assignor toCelanese Corporation of America, a corporation of Delaware ApplicationJanuary 24, 1941, Serial No. 375,761 In Great Britain February 27, 1940Claims.

This invention relates to the production of thermoplastic products andmore particularly to the production of artificial filaments, films,foils and like shaped articles having a basis of thermoplasticcompositions.

Various processes are known for forming shaped articles by extrudingfused thermoplastic compositions, but when working at the hightemperatures generally necessary for these processes, difiiculties havebeen encountered in securing uniform feed of the compositions to theextrusion orifices.

I have now found that very satisfactory feed may be secured if a pump,especially a gear pump, is introduced into the feed pipe for the fusedmaterial, preferably at a point close to the extrusion orifices, and atleast the gland or glands of the pump is maintained in a non-solventmedium at a temperature higher than the fusion point of the composition.Preferably the whole pump is immersed in the hot non-solvent medium.

If it is desired to immerse only the gland or glands of the pump in thenon-solvent medium, a suitable casing may be built round each or all ofthe glands to be immersed and provision made for heating the medium tothe desired degree, especially by electrical heating coils. If desiredthe medium may be circulated through the casing, being heated outsidethe casing. Preferably, means are provided for drawing off liquid fromthe lower part of the casing so that any thermoplastic composition whichescapes through the glands may be readily recovered for return to theprocess.

.As indicated, however, it is preferably to immerse the whole pump inthe hot non-solvent medium, and in such case the medium may be the sameas that into which the thermoplastic composition is to be extruded, forexample according to the process described in U. S. application S. No.369,405, filed December 10, 1940. In this event, provision is made notonly for withdrawing from the medium thermoplastic composition whichescapes through the glands, but also to ensure that such composition isprevented from interfering with the smooth passage of the extrudedmaterials through the medium.

Whether the whole pump or only the glands thereof are maintained at theelevated temperature, it is advantageous to reduce the tendency for thefused thermoplastic composition to escape through the glands byintroducing non-solvent medium into the glands themselves at a pointalong their length under a pressure lower than the minimum pressurewithin the pump so that the medium has no tendency to enter the pumpchamber.

The invention will now be described in greater detail with reference tothe accompanying drawing, in which Fig. 1 is a diagrammatic sideelevation of apparatus in which an immersed pump delivers fused materialto a spinning nozzle immersed in the same fiuid as the pump; and

Fig. 2 is a side elevation of a pump fitted with means for heating thepump gland only.

In Fig. 1, a pump 23 supplied with fused material from a jacketed pipe24 is immersed in nonsolvent liquid in a casing 25 which also serves asa setting bath for the filaments 26 extruded from the nozzle 21 directlyconnected to the pump 23. The liquid is heated by pipes 28 at the bottomof the casing 25. Spent or contaminated liquid may be removed from thecasing through the drain 29 and fresh liquid may be supplied from thepipe 30. The pipes 29, 30 may also be used for continuous circulation offluid through the casing 25.

In Fig. 2, the gland 20 of the pump 1 is surrounded by a casing 3|containing non-solvent liquid. This liquid may be circulated through thecasing by means of pipes 32, 33. An electric element 34 surrounding thecasing 3| provides for the heating of the liquid in the casing.Nonsolvent liquid at lower pressure than that of the fused materialsupplied through the pipe 8 to the pump may be admitted to the glands 20by a pipe 2|.

Pumps for use according to the invention may be made of or lined withany suitable material, due regard being paid to the temperature to whichthey are to be subjected and to the nature of any thermoplasticcomposition which is to contact with them. Examples of suitablematerials, particularly for the surfaces which are exposed to contactwith the compositions, are iron, tin, silver, tantalum, aluminium,copper, and chromium. It will be understood that suitable alloys, e. g.,stainless steel, may also be employed.

For securing uniformity in the extruded materials it is of considerableimportance to ensure good temperature control of the thermoplasticcompositions. Feeding the compositions through narrow tubes isadvantageous for this purpose. Further, strict control must be exercisedover the heating means, whether the composition is heated directly, e.g. by electrical winding round such a narrow tube, or indirectly througha hot fluid medium. Preferably electrical means are employed forheating, either directly or indirectly,

and the electric circuit may include an element of which the resistanceautomatically varies to reduce current as its temperature increases.Such a resistance element, present, for example, in the heated fluidmedium, will operate as a thermostat, and permits the temperature towhich the thermoplastic compositions are subjected to be controlled in aparticularly simple manner. This type of temperature control may beemployed in conjunction with apparatus in which a pump is employed forforwarding the compositions or in which any other method of forwardingis employed.

The temperature to which the glands must be heated will depend largelyupon the nature of the thermoplastic composition which is to beforwarded by the pump. In general, however, temperatures of the order 01ZOO-250 up to 290 or 300 C. are desirable, particularly when employingcompositions which have a basis of superpolymers formed by theself-condensation of aminocarboxylic acids, or by the condensation ofdiamines with dicarboxylic acids.

The present invention may be applied to the extrusion of otherthermoplastic compositions than those referred to in the precedingparagraph, for example, compositions comprising thermoplastic cellulosederivatives, e. g., cellulose acetate, cellulose propionate, cellulosebutyrate, cellulose acetopropionate, cellulose acetobutyrate, ethylcellulose and benzyl cellulose and ether esters of cellulose, polyvinylethers and esters, e. g., polyvinyl acetate and polyvinyl chloracetate,and polymerized esters of unsaturated acids, e. g., those of the acrylicand methacrylic acid series.

The non-solvent medium in which the glands are immersed according to thepresent invention may comprise any substance which is liquid andsubstantially stable at the desired temperature of operation, which isadvantageously the extrusion temperature of the composition. Forexample, it may comprise a hydrocarbon e. g. a paramn or arylatedparamn, acenaphthene, anthracene or an alkyl or aryl derivative ofanthracene, benzene, diphenyl, toluene, a diphenyl-methane ordiphenyl-ethane or an alkyl derivative thereof, naphthalene or an alkylor aryl derivative of naphthalene, including dinaphthyl, phenanthrene,or a compound containing partially or fully hydrogenated aromaticnuclei, e. g., tetralin; an ether, e. g., isoamyl ether, the dimethylether of triethylene glycol, anisol, ethyl benzyl ether, a dinaphthylether, an alkyl naphthyl ether or diphenyl ether; or. ahalogen-substitution derivative of a hydrocarbon or an ether.

While it is preferable to employ liquid media, vaporous or gaseous mediamay also be employed if desired, e. g. the vapours of theabove-mentioned and similar compounds, nitrogen, hydrogen and carbondioxide.

Having described my invention, what I desire to secure by Letters Patentis: e

1. Method of extruding fused thermoplastic compositions, comprisingdelivering a thermoplastic composition to an extruding point by means ofa. feed pump the whole of which, including the gland, is immersed in a,liquid which is a non-solvent for the thermoplastic material of thecomposition, maintaining said liquid at a temperature higher than thefusion point at the composition and extruding said composition by meansof said hot pump into said non-solvent liquid.

2. Method of extruding fused thermoplastic compositions, comprisingdelivering a thermoplastic composition to an extruding point by means ofa feed pump, at least the gland of which is surrounded by a liquid whichis a nonsolvent for the thermoplastic material of the composition,maintaining said liquid at a. tem perature higher than the fusion pointof the composition, introducing said liquid into the gland of the pumpat a superatmospheric pressure lower than the minimum pressure withinthe pump chamber but sufliciently high to minimize leakage into thegland and extruding said composition by means of said pump into said hotnon-solvent liquid.

3. Method of extruding fused thermoplastic compositions, comprisingdelivering a thermoplastic composition to an extruding point by means ofa feed pump the whole of which, in cluding the gland, is immersed in aliquid which is a non-solvent for the thermoplastic material of thecomposition, extruding said composition by means of said pump into saidbody of nonsolvent liquid, circulating said liquid, and electricallyheating said liquid to a temperature higher than the fusion point of thecomposition.

4. Method of extruding fused thermoplastic compositions, comprisingdelivering a thermoplastic composition to an extruding point by means ofa feed pump the whole of which, including the gland, is immersed in aliquid which is a non-solvent for the thermoplastic material of thecomposition, maintaining said liquid at a temperature higher than thefusion point of the composition, introducing said liquid into the glandof the pump at a superatmospheric pressure lower than the minimumpressure within the pump chamber but sufiiciently high to minimizeleakage into the gland and extruding said composition by means of saidpump into said hot non-solvent liquid.

5. Method of extruding fused thermoplastic compositions, comprisingdelivering a thermoplatic composition to an extruding point by means ofa feed pump, at least the gland of which is surrounded by a liquid whichis a nonsolvent for the thermoplastic material of the composition,electrically heating said non-solvent liquid so as to maintain it at atemperature higher than the fusion point of the composition, circulatingsaid liquid, introducing said liquid into the gland of the pump at asuperatmospheric pressure lower than the minimum pressure within thepump chamber but sufflciently high to minimize leakage into the glandand extruding said composition by means of said pump into said hotnon-solvent liquid.

HENRY DREYFUS.

